Slow cranking 5.7 Vortec... stumped here.

[Velislide]

Awhile back I picked this truck up, and have dumped a ton of money into it, just to get caught back up on all the maintenance and fixing what has been neglected.

Now when I first got the truck, it cranked pretty slow but had a marine battery installed. Being winter, I changed out the battery with a new 800cca one. Still cranked slow, engine would almost sound like it has too much compression for the starter, so I installed a new direct drive starter now. Still does it after the truck warms up, but usually cranks fine cold. Now I replaced the crank position sensor with a new AC Delco sensor, didn't have any high idle issues after installing the new sensor, so that's good, guessing it didn't need to relearn? But STILL has the slow crank issue when warm. It gets so slow cranking, it basically stops and the starter drive gear pops off the flywheel and spins against the flywheel face.

I've done a ton of work to this truck, to get it running as nice as it does now. What could be going on here? My next guess is battery and starter cables? But they didn't look too terrible. Or are these direct drive starters junk? Maybe thinking of bringing it back and getting a gear reduction starter.

Was thinking heat soak could possibly be an issue? Since the starter doesn't have a heat shield. But I only drove it maybe 5 miles to get it up to temp, and it starts cranking extremely slow.

 

[21Actual]

Clean and confirm all large ground connections are in good shape. Block to frame, starter to block, battery to frame. I like to add a 2 gauge ground from battery neg to engine block for good measure. Ground that sucker good..

 

[michael hurd]

It could literally be anything. I would suggest cleaning all of the grounds as the previous poster suggested.

Do you have any coolant losses?

Pull the belt off of the truck, and give the tensioner and idler pulley a spin... rough, noisy?

Give the water pump pulley a spin by hand... how's that, same with the power steering pump and A/C compressor... is your A/C clutch stuck applied or bearing toast?

 

[ram1220]

I had a similar issue with my 90 5.7l TBI a few months ago. I put a brand new battery in and after a few days the truck would crank extremely slow. I ended up cleaning the connections on the battery cables. I could only see a tiny bit of corrosion. I thought it couldn't be enough to cause the problem but it was. Once cleaned and a good charge of the battery all is good.

 

[slowburb]

Sounds like wiring is corroded and can't carry volts/amps through starting system. The stock starter is a good starter, and is gear reduction, not direct drive. There was probably nothing wrong with yours. I'd go for new cables at battery/alternator/starter/pcm.

 

[SAATR]

Voltage drop test at the starter before you replace anything. That way you know what the issue is and aren't just firing the parts cannon at the problem. It's as simple as hooking a multimeter to the starter supply post at the starter and the ground lead to the block. If you lose more than 1 volt between measurements taken at the battery while cranking and at the starter while cranking, you've got excessive resistance in the circuit do to poor connections or corroded wires and should replace them.

Sent from my XT1585 using Tapatalk

 

[RyanMerrick]

Good advice above... I found my frame to block grounding strap completely rusted through last summer.

 

[Velislide]

Sounds good. I'll check out my cables and what not, Minnesota rust doesn't help things at all. And this starter is the Direct Drive unit, not Gear reduced. It was what was installed, so I could get my core exchange money back. Only 90$ after, though wishing I bought a gear reduction starter instead.

 

[Rogue]

Did you ever find the issue, Velislide? I'm having a similar issue, except I've never replaced my starter yet. Gonna start cleaning connections on wires regardless....

 

[Velislide]

Funny that I didn't even realize this was my post. Still having the issue. New engine, new starter, all new grounds, and battery cables. Still has the slow crank issue. Almost sounds like the battery is dead sometimes when you try to crank, it cranks so slow. I guess maybe that's just how these crank? Tried another battery also, same thing.